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Spiral ring reveals ancient complex machines

Distinctive spiral patterns carved into a small jade ring show that China was using complex machines more than 2500 years ago, says a Harvard graduate student in physics.

The spiral-patterned ring is 27 millimetres in diameter and was probably a body ornament

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The ring was among the goods found in high-status graves from China’s “Spring and Autumn Period” from 771 to 475 BC. Most archaeological attention has focused on larger and more spectacular jade and bronze artifacts. But Peter Lu identified the patterns on the small rings as Archimedes’ spirals, which he believes are the oldest evidence of compound machines.

Simple machines that move in only one way date back at least 5000 years, to the invention of the potter’s wheel. But it took much longer to invent compound machines, which precisely convert motion from one kind into another.

Archimedes is sometimes credited with building an undescribed compound machine to move ships in the harbour of Syracuse in the third century BC, but the earliest well-accepted descriptions were by Hero of Alexandria in the first century AD.

Old record player

Specialists believe most ancient Chinese jades were hand-carved, but Lu thought the spirals on the jade rings were machine-made as soon as Jenny So, an art historian at the Chinese University of Hong Kong, showed him one at the Smithsonian Institution.

“I said I bet you could do it with a modified bow drill, and she looked at me as if I had two heads,” Lu told New Scientist.

Challenged to prove he was right, Lu built a spiral-carving machine around an old record player. It resembles the bow drill that Boy Scouts traditional use to start fires without matches.

The fixed stylus writes a spiral on the surface

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He wrapped a string tightly around the spindle on the turntable, and attached its ends to a rod that ran between mounts on either side of the turntable (see diagram). Holes in the mounts held the rod so it could move back and forth along its length, but not sideways. A stylus attached to the rod rested on the turntable. Moving the rod back and forth turned the turntable, so the fixed stylus wrote a spiral on the surface.

Circumstantial evidence

“There is no prima face evidence that this is how they did it,” Lu admits. But the circumstantial evidence is strong.

The spirals neatly match the Archimedian shape, and their center is at the centre of the ring, which could be cut that way by turning the jade with the stylus fixed in place. The spiral carvings are also noticeably more uniform than other jade patterns.

The rings date from at least 552 BC, and while there is no evidence of earlier spiral rings, Lu says nobody has been looking for them.

Meanwhile, Lu is turning back to his graduate work in physics. On Friday he has to talk to astronauts on the International Space Station about an experiment he has on board to study how liquids and gases change phase.